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Abstract:

A vision prosthesis includes an optical element having a characteristic
function associated with refraction therethrough. The characteristic
function is selected to reduce aberration in an eye when the optical
element is implanted at a location therein.

Claims:

1. A method, comprising: implanting an optical element into an eye;
measuring aberration in the eye when the optical element is implanted in
the eye; selecting a high-order aberration correction, represented by
wavefront data determined based on the measured aberration, to modify a
characteristic function associated with refraction through the optical
element to reduce high-order aberration in the eye when the optical
element is implanted at a location therein; incorporating into the
wavefront data dependence of the high-order aberration correction on an
estimate of a distance to an object-of-regard based on predicted changes
to optical path lengths in the eye that occur during accommodation; and
applying the high-order aberration correction to the optical element.

2. The method of claim 1, wherein applying the high-order aberration
correction to the optical element comprises storing the wavefront data in
a memory element in electrical communication with the optical element.

3. The method of claim 1, wherein the wavefront data stored in the memory
element is used to control an index of refraction profile of the optical
element.

4. The method of claim 3, wherein the index of refraction profile of the
optical element is modifiable to reduce a different high-order aberration
in response to different wavefront data being stored in the memory
element.

5. The method of claim 1, wherein the high-order aberration correction is
based on a first wavefront aberration measurement of anatomical features
of a patient's eye while the patient is focusing on an object at a first
distance and based on a second wavefront aberration measurement of the
anatomical features of the eye while the patient is focusing on an object
at a second distance different from the first distance.

6. The method of claim 5, wherein the first and second wavefront
aberration measurements are used to provide wavefront data that provides
high-order aberration correction that depends on an estimate of a
distance to an object-of-regard.

7. The method of claim 4, wherein the wavefront data, when configured
according to a first selected high-order aberration correction, modifies
the characteristic function based on a first predetermined position or
orientation for the optical element within the eye.

8. The method of claim 7, wherein the wavefront data, when configured
according to a second selected high-order aberration correction, modifies
the characteristic function based on a second predetermined position or
orientation for the optical element within the eye.

9. The method of claim 8, wherein the second selected high-order
aberration correction includes adjustments based on postoperative
deviations in the second position or orientation of the optical element
from the first predetermined position or orientation.

10. The method of claim 1, wherein the location in the eye is selected
from the group consisting of: the anterior chamber; the posterior
chamber; the lens-bag; and the cornea.

11. The method of claim 1, wherein the optical element is implanted in a
phakic human patient.

12. The method of claim 1, wherein the optical element is implanted in an
aphakic human patient.

13. The method of claim 1, wherein the high-order aberration comprises at
least one of spherical aberration, coma, field curvature, and distortion.

14. A vision prosthesis for implantation in an eye, the vision prosthesis
comprising: an optical element having a characteristic function
associated with refraction therethrough; and a memory element that stores
wavefront data representing a high-order aberration correction selected
based on aberration in the eye that was measured when the optical element
was implanted in the eye, the high-order aberration correction being
selected to modify the characteristic function associated with refraction
through the optical element to reduce high-order aberration in the eye
when the optical element is implanted at a location therein; a
range-finder configured to provide an estimate of a distance to an
object-of-regard; and an actuator configured to apply the high-order
aberration correction to the optical element; wherein the wavefront data
incorporates dependence of the high-order aberration correction on the
estimate based on predicted changes to optical path lengths in the eye
that occur during accommodation.

15. The vision prosthesis of claim 14, wherein the wavefront data stored
in the memory element is used to control an index of refraction profile
of the optical element.

16. The vision prosthesis of claim 15, wherein the index of refraction
profile of the optical element is modifiable to reduce a different
aberration in response to different wavefront data being stored in the
memory element.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation application of and claims
priority to U.S. application Ser. No. 12/542,143, filed on Aug. 17, 2009,
which is a divisional application and claims priority to U.S. application
Ser. No. 10/712,294, filed on Nov. 13, 2003, the entire contents of which
are incorporated herein by reference.

FIELD OF INVENTION

[0002] The invention relates to an aberration correcting vision
prosthesis.

BACKGROUND

[0003] In the course of daily life, one typically regards objects located
at different distances from the eye. To selectively focus on such
objects, the focal length of the eye's lens must change. In a healthy
eye, this is achieved through the contraction of a ciliary muscle that is
mechanically coupled to the lens. To the extent that the ciliary muscle
contracts, it deforms the lens. This deformation changes the focal length
of the lens. By selectively deforming the lens in this manner, it becomes
possible to focus on objects that are at different distances from the
eye. This process of selectively focusing on objects at different
distances is referred to as "accommodation."

[0004] As a person ages, the lens loses plasticity. As a result, it
becomes increasingly difficult to deform the lens sufficiently to focus
on objects at different distances. This condition is known as presbyopia.
Refractive errors caused by such conditions as hyperopia, myopia, as well
as aberrations due to irregularities in the eye (e.g., in the cornea or
in the natural crystalline lens) can also cause problems in one's ability
to focus on an object. To compensate for this loss of function, it is
useful to provide different optical corrections for focusing on objects
at different distances. Some restoration of focusing ability for some
distances can be provided by spectacles or contact lenses.

[0005] There are also a variety of disorders that degrade the ability of
the eye to function properly. These include vitreoretinal disorders,
lenticular disorders, corneal disorders, and glaucomatous states. Some
treatments to some of these types of disorders involve surgical
intervention. For example, a common disorder involves progressive
clouding of the natural crystalline lens resulting in the formation of
what is referred to as a cataract. A common practice used to treat a
cataract is surgically removing the cataractous natural crystalline lens
and implanting (in the "aphakic" patient) an artificial intraocular lens
into the empty lens bag to replace the natural crystalline lens. After
cataract surgery, the corneal incision (and/or limbal and scleral
incisions) can potentially induce optical aberrations due to altered
corneal curvature and topography. Intraocular lenses can also be used for
a "phakic" patient who still has a natural crystalline lens.

SUMMARY

[0006] In one aspect, the invention features a vision prosthesis including
an optical element having a characteristic function associated with
refraction therethrough. The characteristic function is selected to
reduce aberration in an eye when the optical element is implanted at a
location therein.

[0007] In one embodiment the vision prosthesis includes a modifiable part
for selectively modifying the characteristic function of the optical
element.

[0008] The modifiable part can include a wavefront component that is
releasably attachable to the optical element, and the wavefront component
has a surface shaped to reduce the aberration in the eye. The shape of
the surface is formed using wavefront-guided laser ablation. The
wavefront component and the optical element have relative orientation
features.

[0009] Alternatively, the modifiable part can include a memory element in
the vision prosthesis. The memory element stores modifiable wavefront
data selected to control an index of refraction profile of the optical
element to reduce the aberration in the eye.

[0010] Alternatively, the modifiable part can include a deformable
material whose shape is configured to change in response to an actuator.

[0011] In another embodiment, the vision prosthesis includes a
range-finder for generating, from a stimulus, an estimate of a distance
to an object-of-regard. An actuator in communication with the optical
element provides a signal that controls the focusing power of the optical
element. A controller is coupled to the rangefinder and to the actuator,
for causing the actuator to generate the signal based on the estimate.

[0012] In another embodiment, the vision prosthesis includes an actuator
in communication with the optical element for providing a signal that
controls the characteristic function of the optical element. A controller
is coupled to the actuator for causing the actuator to generate the
signal based on wavefront data stored in a memory element of the
controller.

[0013] The signal can be a parallel signal carried over a plurality of
signal lines addressing a corresponding plurality of electrodes on the
actuator. The characteristic function of the optical element changes in
response to the signal by changing an index of refraction of material
within the optical element at a plurality of locations.

[0014] Alternatively, the characteristic function of the optical element
changes in response to the signal by changing shape of a surface of the
optical element.

[0015] In some embodiments, the vision prosthesis includes a range-finder
coupled to the controller for generating, from a stimulus, an estimate of
a distance to an object-of-regard. The signal is based on the estimate,
and the focusing power and/or characteristic function of the optical
element changes in response to the estimate. When implanted in the eye,
the optical element can be disposed at a variety of locations, such as
the anterior chamber, the posterior chamber, the lens-bag, and the
cornea.

[0016] The vision prosthesis can be adapted for implantation in a phakic
human patient, or for implantation in an aphakic human patient.

[0017] In another aspect, the invention features a method including
implanting an optical element into an eye, measuring aberration in the
eye when the optical element is implanted in the eye, determining
wavefront data based on the measured aberration, and programming the
wavefront data into a memory device in electrical communication with the
optical element. A characteristic function associated with refraction
through the optical element is designed to reduce aberration in the eye
after the memory device is programmed.

[0018] In another aspect, the invention features a method including
implanting an optical element into an eye, measuring aberration in the
eye when the optical element is implanted in the eye, shaping a wavefront
component based on the measured aberration, inserting the wavefront
component into the eye, and attaching the wavefront component to the
optical element. A characteristic function associated with refraction
through the optical element is designed to reduce aberration in the eye
after the wavefront component is attached.

[0019] As used herein, "aberration" means any one or combination of
low-order or high-order aberration (including spherical aberration, coma,
astigmatism, field curvature, and distortion), or chromatic aberration.

[0020] As used herein, a "characteristic function" means a function such
as a point characteristic, an angle characteristic, or a mixed
characteristic that describes refraction of a wavefront of light through
a medium.

[0021] Unless otherwise defined, all technical and scientific terms used
herein have the same meaning as commonly understood by one of ordinary
skill in the art to which this invention belongs. Although methods and
materials similar or equivalent to those described herein can be used in
the practice or testing of the present invention, suitable methods and
materials are described below. All publications, patent applications,
patents, and other references mentioned herein are incorporated by
reference in their entirety. In case of conflict, the present
specification, including definitions, will control. In addition, the
materials, methods, and examples are illustrative only and not intended
to be limiting.

[0022] Other features and advantages of the invention will become apparent
from the following description, and from the claims.

[0024]FIG. 2 shows an embodiment of the vision prosthesis of FIG. 1 using
a controller to provide wavefront correction.

[0025]FIG. 3 shows another embodiment of the vision prosthesis of FIG. 1
using a wavefront component to provide wavefront correction.

[0026]FIG. 4 is a procedure for preparing and implanting the vision
prosthesis of FIG. 3.

[0027]FIG. 5 shows a feedback mechanism for a rangefinder of the vision
prosthesis of FIG. 1.

DESCRIPTION

[0028]FIG. 1 shows a block diagram of a vision prosthesis 10 having an
optical element 12 whose focusing power can be made to vary in response
to a signal provided to the optical element 12 by an actuator 14.
Techniques for changing the focusing power of the optical element 12
include changing the shape and/or index of refraction of material within
the optical element. In one implementation, the optical element 12
includes a nematic liquid-crystal whose index of refraction varies in
response to an applied electric field, and the actuator 14 includes one
or more electrodes in electrical communication with the optical element
12. Alternatively, the optical element 12 collects light through a
material whose index of refraction varies in response to an applied
magnetic field. In this case, the actuator 14 is a magnetic field source,
such as a current-carrying coil, in magnetic communication with the
optical element 12. In addition, to or instead of, a change in index of
refraction, the shape of a movable surface of the optical element 12
changes (e.g., chemically or mechanically) in response to the signal
provided by the actuator 14. In another embodiment, the optical element
includes a movable component for focusing. In this case, the actuator 14
moves one or more lenses or lens components along the visual axis to
change the focal length of the optical element 12.

[0029] The vision prosthesis 10 provides accommodative adjustments and
corrects for wavefront aberrations present in a patient's eye (e.g., due
to abnormalities in the cornea, the natural crystalline lens, or the
ocular media). The nature of the signal provided by the actuator 14
controls the extent to which a shape and/or index of refraction of the
optical element 12 is changed and the corresponding level of
accommodation. The actuator 14 generates a signal in response to
instructions from a controller 16 in communication with the actuator 14.
Corrections for wavefront aberrations in the eye can be made based on
wavefront data stored in a memory device 17 in the controller 16.
Alternatively, wavefront corrections can be made using a wavefront
component 13 attached to the optical element 12. Either of these
techniques can be used, alone or in combination. Both techniques are
described in more detail below.

[0030] The controller 16 is typically a microcontroller having
instructions encoded therein. These instructions can be implemented as
software or firmware. However, the instructions can also be encoded
directly in hardware in, for example, an application-specific integrated
circuit. The instructions provided to the microcontroller include
instructions for receiving, from a range-finder 18, data indicative of
the distance-of-regard (i.e., distance to an object-of-regard), and
instructions for processing that data to obtain a signal for focusing,
and optionally, for wavefront aberration correction. The actuator 14 uses
the signal to alter the optical element's properties to focus an
aberration-corrected image of the object-of-regard on the retina.

[0031] The rangefinder 18 typically includes a transducer 19 for detecting
a stimulus from which a range to an object can be inferred. The signal
generated by the transducer 19 often requires amplification before it is
of sufficient power to provide to the controller 16. Additionally, the
signal may require some preliminary signal conditioning. Accordingly, in
addition to a transducer 19, the rangefinder 18 includes an amplifier 21
to amplify the signal, an A/D converter 23 to sample the resultant
amplified signal, and a digital signal processor 25 to receive the
sampled signal. The digital signal processor 25 optionally performs
signal conditioning (e.g., noise reduction or pattern matching). The
output of the digital signal processor 25 is provided to the controller
16.

[0032] A power source 20 supplies power to the controller 16, the range
finder 18, and the actuator 14. A single power source 20 can provide
power to all three components. However, the vision prosthesis 10 can also
include a separate power source 20 for any combination of those
components that require power.

Wavefront Correction

[0033] To correct for wavefront aberrations, the change in shape, or index
of refraction, of the optical element 12 is made a function of more than
one spatial variable. By providing a plurality of actuating elements
coupled to different local regions of the optical element 12 (e.g.,
distributed in a polar grid or a rectilinear grid), the optical path
length through the optical element 12 can be varied at those local
regions. For example, electrodes can apply a field to change the local
refractive index, or mechanical actuators can apply force to deform local
regions of a reflecting or refracting surface. An artificial muscle
system (e.g., based on contractile polymers) can be used to change the
shape of an optical element 12 to reduce wavefront aberrations.

[0034] A wavefront of light passing through the optical element 12 will be
altered in a way that can be described by a characteristic function
associated with refraction through the optical element 12. The
characteristic function of an optical element can be estimated from
knowledge of the optical path length traversed by any ray of light
passing through any portion of the element. For an optical element
comprised of various media having various surfaces, the optical path
length can be determined from the index of refraction within the various
media and the shapes of its surfaces. This type of analysis can also be
used to design and construct an optical element having a desired
characteristic function.

[0035] By measuring any pre-existing aberrations in a patient's eye, the
optical element 12 can be designed to have a characteristic function that
counters the effects of pre-existing aberrations. As a result, an optical
element 12 implanted at a location intersecting the eye's visual axis
reduces any remaining aberrations compared to the pre-existing
aberrations. The optical element 12 can be located at any of a variety of
locations including in front of the iris 26, sutured to the iris 26,
hooked to the iris 26, sutured to the sulcus, or in the lens-bag 22.

Programmable Wavefront Correction

[0036] Referring to FIG. 2, in one embodiment of the vision prosthesis 10,
the optical the optical element 12 is implanted into the lens-bag 22 of
an aphakic patient. For a phakic patient, the optical element 12 is
implanted behind the iris 26 in the posterior chamber 24, in front of the
iris 26 in the anterior chamber 34, or in the cornea 36. As described in
connection with FIG. 1, a transducer 19 transfers an electrical or
mechanical stimulus from the eye through an amplifier 21, an A/D
converter 23, and a digital signal processor 25, to a controller 16, all
of which are located at the periphery of the optical element 12. A
range-finder 18 can include one or more transducers 19 that sense stimuli
from any of a variety of locations, such as the ciliary muscle 54, the
zonules 56, or the lens-bag 22, as described in more detail below. A
power source 20 can include a battery 68 under the conjunctiva 70 and/or
a photovoltaic cell 72 at the periphery of the optical element 12 (e.g.,
in an annulus), also described in more detail below.

[0037] The controller 16 includes wavefront data (stored in a memory
device 17) based on a wavefront aberration measurement performed on a
patient. The optical element 12 includes an artificial intraocular lens
that changes its shape and/or index of refraction over a two-dimensional
surface or grid in response to a signal from the actuator 14. The
controller 16 uses the wavefront data to determine point-by-point (over
the two-dimensional surface or grid) the signal provided by the actuator
14 in response to the output of the range-finder 18.

[0038] To measure wavefront aberrations in a patient's eye, a surgeon
measures anatomical features of the eye. For a patient undergoing
cataract surgery (i.e., removal of part or all of the natural crystalline
lens), it is useful to obtain measurements that do not change after the
cataract surgery. For example, valid measurements can be obtained from
axial lengths of structures of the eye (including the depth of the
anterior chamber 34), corneal topography, and influence of certain
incisions (e.g., corneal, scleral, or corneoscleral) on corneal
topography.

[0039] These measurements are used to predict wavefront aberrations in the
eye after cataract surgery. An ideal shape and/or index of refraction
across the light collecting portion of the optical element 12, that
corrects the predicted wavefront aberrations, is obtained by generating
wavefront data based on the predicted wavefront aberrations.

[0040] The resulting wavefront corrections may be different for different
distances-of-regard. The wavefront data should therefore depend on
distance of regard. One way to accomplish this is by performing separate
measurements of the anatomical features of the eye while the patient is
focusing on objects at different distances. Another way to obtain
wavefront data that depend on distance-of-regard is to incorporate the
dependence into the wavefront data based on theoretical calculations of
predicted changes to optical path lengths in the eye that occur during
accommodation (e.g., changes to the natural crystalline lens for a phakic
patient or changes to an artificial intraocular lens in an aphakic
patient). The controller 16 can then use the wavefront data to cause the
actuator 14 to provide different signals for different range estimates
provided by the range-finder 18, thereby correcting wavefront aberration
in a manner that depends in part on what the patient is looking at.

[0041] The wavefront data are also calculated based on predetermined
position and orientation for the optical element within the patient's
eye. After preparing components of the vision prosthesis, the surgeon
implants the prosthesis as close as possible to the predetermined
position and orientation within the patient's eye. If a patient is also
undergoing cataract surgery and wavefront data in the controller 16 are
based on measurements before the patient's natural crystalline lens has
been removed, adjustments can be made based on measurements of
postoperative deviations due to removal of the natural crystalline lens.
Adjustments can also be made based on postoperative deviations in the
position or orientation of the optical element 12 from the predetermined
position and orientation. The wavefront data can also be updated based on
changes that occur in the patient's vision (e.g., due to healing after
surgery or aging).

[0042] Such adjustments can be performed, for example, by removing the
controller 16, re-programming it with new wavefront data, and replacing
it. Alternatively, the controller 16 can be re-programmed in situ by
transmitting data over an encrypted wireless link (e.g., an infrared
beam). The controller 16 uses encryption to ensure that only an
authorized user (e.g., a surgeon) can gain access to the wavefront data
(e.g., for updating or testing).

Ablated Surface Wavefront Correction

[0043] In another embodiment, shown in FIG. 3, the wavefront correction is
implemented by a releasably attachable wavefront component 13. In this
embodiment, the optical element 12 is placed in a patient's eye (along
with an actuator 14, controller 16, and range-finder 18) in a first
surgical procedure. After the first surgical procedure, measurements of
wavefront aberrations of the postoperative eye are taken. These
measurements are used to perform wavefront-guided laser ablation on a
surface 40 of a wavefront component 13. In a second surgical procedure,
the wavefront component 13 is mated with the optical element 12 at a
predetermined location. The wavefront component 13 is designed for a
particular distance-of-regard (e.g., an average or preferred distance).
However, the wavefront component 13 can be easily replaced with another
wavefront component designed for a different distance-of-regard.

[0044] In the second surgical procedure, the wavefront component 13 is
folded and inserted through a small incision, maneuvered into the desired
location, and released. Once released, the component 13 springs back to
its unfolded position. Since the second surgical procedure is less
invasive than the first surgical procedure, it is less likely to induce
further aberrations than the first surgical procedure.

[0045] The optical element 12 mates with the wavefront component 13 in
such a way that the wavefront component 13 is in a predetermined position
and orientation relative to the optical element 12. The optical element
12 and the wavefront component 13 have relative orientation features,
such as at least two asymmetrically placed positioning holes 42 on the
optical element and corresponding tabs 44 on the wavefront component 13.
A specialized surgical tool can be used to facilitate engagement or
replacement of the wavefront component 13. Alternative techniques for
mating the wavefront component 13 to the optical element 12 include
spinning the wavefront component 13 into a specialized groove, unfolding
the wavefront component 13 into raised hooks, or connecting the wavefront
component 13 to another component, such as a transducer 19.

[0046] The ablated surface 40 of the wavefront component 13 is shaped to
correct for the wavefront aberrations present in the eye after the first
surgical procedure. Laser ablation can be performed using an excimer
laser on a wavefront component 13 composed of a material such as
polymethyl methacrylate (PMMA) or acrylic. Alternatively, the wavefront
component 13 can be etched to the desired shape using mechanical or
photochemical etching. The resulting surface 40 of the wavefront
component 13 is shaped to correct for wavefront aberrations when
positioned in the eye, taking into account the difference between the
index of refraction of the material of the wavefront component 13 and the
index of refraction of the aqueous humor inside the eye.

[0047] Referring to FIG. 4, an exemplary procedure 46 for implanting the
vision prosthesis shown in FIG. 3 includes implanting 48 the optical
element 12 into the eye in the first surgical procedure. After the
optical element 12 is implanted, the procedure 46 includes measuring 49
any aberration in the eye, including any effects of the optical element
12. Based on the measured aberrations, laser-ablation is used to shape 50
a surface of the wavefront component 13 to reduce aberration in the eye
after the wavefront component 13 is installed. The wavefront component 13
is installed by inserting 51 the folded wavefront component 13 into a
small incision in the eye and attaching 52 the unfolded wavefront
component 13 to the optical element 12.

Rangefinder

[0048] In a normal eye, contraction of a ciliary muscle 54 is transmitted
to the natural crystalline lens by zonules 56 extending between the
ciliary muscle 54 and the lens-bag 22. When an object-of-regard is
nearby, the ciliary muscle 54 contracts, thereby deforming the natural
crystalline lens so as to bring an image of the object into focus on the
retina. When the object-of-regard is distant, the ciliary muscle 54
relaxes, thereby restoring the natural crystalline lens to a shape that
brings distant objects into focus on the retina. The activity of the
ciliary muscle 54 thus provides an indication of the range to an
object-of-regard.

[0049] The transducer 19 of the rangefinder 18 can be a transducer for
detecting contraction of the ciliary muscle 54. In one implementation,
the rangefinder 18 can include a pressure transducer that detects the
mechanical activity of the ciliary muscle 54. A pressure transducer
coupled to the ciliary muscle 54 can be a piezoelectric device that
deforms, and hence generates a voltage, in response to contraction of the
ciliary muscle 54. In another implementation, the transducer 19 can
include an electromyograph for detecting electrical activity within the
ciliary muscle 54.

[0050] As noted above, the activity of the ciliary muscle 54 is
transmitted to the natural crystalline lens by zonules 56 extending
between the ciliary muscle 54 and the lens-bag 22. Both the tension in
the zonules 56 and the resulting mechanical disturbance of the lens-bag
22 can be also be used as indicators of the distance to the
object-of-regard. In recognition of this, the rangefinder 18 can also
include a tension measuring transducer in communication with the zonules
56 or a motion sensing transducer in communication with the lens-bag 22.
These sensors can likewise be piezoelectric devices that generate a
voltage in response to mechanical stimuli.

[0051] The activity of the rectus muscles 58 can also be used to infer the
distance to an object-of-regard. For example, a contraction of the rectus
muscles 58 that would cause the eye to converge medially can suggest that
the object-of-regard is nearby, whereas contraction of the rectus muscles
58 that would cause the eye to gaze forward might suggest that the
object-of-regard is distant. The rangefinder 18 can thus include a
transducer 19 that responds to either mechanical motion of the rectus
muscles 58 or to the electrical activity that triggers that mechanical
motion.

[0052] It is also known that when a person intends to focus on a nearby
object, the iris 26 contracts the pupil 60. Another embodiment of the
rangefinder 18 relies on this contraction to provide information
indicative of the distance to the object-of-regard. In this embodiment,
the rangefinder 18 includes a transducer 19, similar to that described
above in connection with the rangefinder 18 that uses ciliary muscle or
rectus muscle activity, to estimate the distance to the object-of-regard.
Additionally, since contraction of the pupil 60 diminishes the light
incident on the optical element 12, the transducer 19 of the rangefinder
18 can include a photodetector for detecting this change in the light.

[0053] The foregoing embodiments of the rangefinder 18 are intended to be
implanted into a patient, where they can be coupled to the anatomical
structures of the eye. This configuration, in which the dynamic
properties of one or more anatomical structures of the eye are used to
infer the distance to an object-of-regard, is advantageous because those
properties are under the patient's control. As a result, the patient can,
to a certain extent, provide feedback to the rangefinder 18 by
controlling those dynamic properties. For example, where the rangefinder
18 includes a transducer responsive to the ciliary muscle 54, the patient
can control the index of refraction of the optical element 12 by
appropriately contracting or relaxing the ciliary muscle 54.

[0054] Other embodiments of the rangefinder 18 can provide an estimate of
the range without relying on stimuli from anatomic structures of the eye.
For example, a rangefinder 18 similar to that used in an auto-focus
camera can be implanted. An example of such a rangefinder 18 is one that
transmits a beam of infrared radiation, detects a reflected beam, and
estimates range on the basis of that reflected beam. The output of the
rangefinder 18 can then be communicated to the actuator 14. Since a
rangefinder 18 of this type does not rely on stimuli from anatomic
structures of the eye, it need not be implanted in the eye at all.
Instead, it can be worn on an eyeglass frame or even hand-held and
pointed at objects of regard. In such a case, the signal from the
rangefinder 18 can be communicated to the actuator 14 either by a wire
connected to an implanted actuator 14 or by a wireless link.

[0055] A rangefinder 18 that does not rely on stimuli from an anatomic
structure within the eye no longer enjoys feedback from the patient. As a
result, it is desirable to provide a feedback mechanism to enhance the
range-finder's ability to achieve and maintain focus on an
object-of-regard.

[0056] In a feedback mechanism as shown in FIG. 5, first and second
lenslets 62a, 62b are disposed posterior to the optical element 12. The
first and second lenslets 62a, 62b are preferably disposed near the
periphery of the optical element 12 to avoid interfering with the
patient's vision. A first photodetector 64a is disposed at a selected
distance posterior to the first lenslet 62a, and a second photodetector
64b is disposed at the same selected distance posterior to the second
lenslet 62b. The focal length of the first lenslet 62a is slightly
greater than the selected distance, whereas the focal length of the
second lenslet 62b is slightly less than the selected distance.

[0057] The outputs of the first and second photodetectors 64a, 64b are
connected to a differencing element 66 that evaluates the difference
between their output. This difference is provided to the digital signal
processor 25. When the output of the differencing element 66 is zero, the
optical element 12 is in focus. When the output of the differencing
element 66 is non-zero, the sign of the output identifies whether the
focal length of the optical element 12 needs to be increased or
decreased, and the magnitude of the output determines the extent to which
the focal length of the optical element 12 needs to change to bring the
optical element 12 into focus. A feedback mechanism of this type is
disclosed in U.S. Pat. No. 4,309,603, the contents of which are herein
incorporated by reference.

[0058] In any of the above embodiments of the rangefinder 18, a manual
control can also be provided to enable a patient to fine-tune the
focusing signal. The digital signal processor 25 can then use any
correction provided by the user to calibrate the range estimates provided
by the rangefinder 18 so that the next time that that range estimate is
received, the focusing signal provided by the digital signal processor 25
will no longer need fine-tuning by the patient. This results in a
self-calibrating vision prosthesis 10.

[0059] The choice of which of the above range-finders is to be used
depends on the particular application. For example, an optical element 12
implanted in the posterior chamber 24 has ready access to the ciliary
muscle 54 near the transducer 19. Under these circumstances, a
rangefinder that detects ciliary muscle activity is a suitable choice. An
optical element 12 implanted in the anterior chamber 34 is conveniently
located relative to the iris 26 but cannot easily be coupled to the
ciliary muscle 54. Hence, under these circumstances, a rangefinder that
detects contraction of the iris 26 is a suitable choice. An optical
element 12 implanted in the cornea 36 is conveniently located relative to
the rectus muscles 58. Hence, under these circumstances, a rangefinder
that detects contraction of the rectus muscles 58 is a suitable choice.
In the case of an aphakic patient, in which the natural crystalline lens
in the lens-bag 22 has been replaced by an optical element 12, a
rangefinder that detects zonule tension or mechanical disturbances of the
lens-bag 22 is a suitable choice. In patients having a loss of function
in any of the foregoing anatomical structures, a rangefinder that
incorporates an automatic focusing system similar to that used in an
autofocus camera is a suitable choice.

Power Source

[0060] As noted above, the controller 16, the rangefinder 18, and the
actuator 14 shown in FIG. 1 use a power source 20. In one embodiment, the
power source 20 can be an implanted battery 68. The battery 68 can be
implanted in any convenient location, such as under the conjunctiva 70 in
the Therron's capsule, or within the sclera. Unless it is rechargeable in
situ, such a power source 20 will periodically require replacement.

[0061] In another embodiment, the power source 20 can be a photovoltaic
cell 72 implanted in a portion of the eye that receives sufficient light
to power the vision prosthesis 10. The photovoltaic cell 72 can be
mounted on a peripheral portion of the optical element 12 where it will
receive adequate light without interfering excessively with vision.
Alternatively, the photovoltaic cell can be implanted within the cornea
36, where it will receive considerably more light. When implanted into
the cornea 36, the photovoltaic cell 72 can take the form of an annulus
or a portion of an annulus centered at the center of the cornea 36. This
configuration avoids excessive interference with the patient's vision
while providing sufficient area for collection of light.

[0062] Power generated by such a photovoltaic cell 72 can also be used to
recharge a battery 68, thereby enabling the vision prosthesis 10 to
operate under low-light conditions. The use of a photovoltaic cell as a
power source 20 eliminates the need for the patient to undergo the
invasive procedure of replacing an implanted battery 68.

[0063] The choice of a power source 20 depends in part on the relative
locations of the components that are to be supplied with power and the
ease with which connections can be made to those components. When the
optical element 12 is implanted in the cornea 36, for example, the
associated electronics are likely to be accessible to a photovoltaic cell
72 also implanted in the cornea 36. In addition, a rechargeable
subconjunctival battery 68 is also easily accessible to the photovoltaic
cell 72. The disposition of one or more photovoltaic cells 72 in an
annular region at the periphery of the cornea 36 maximizes the exposure
of the photovoltaic cells 72 to ambient light.

[0064] When the optical element 12 is implanted in the anterior chamber
34, one or more photovoltaic cells 72 can be arranged in an annular
region on the periphery of the optical element 12. This reduces
interference with the patient's vision while providing sufficient area
for exposure to ambient light. For an optical element 12 implanted in the
anterior chamber 34, a rechargeable battery 68 implanted beneath the
conjunctiva 70 continues to be conveniently located relative to the
photovoltaic cells 72.

[0065] When the optical element 12 is implanted in the posterior chamber
24, one or more photovoltaic cells 72 can be arranged in an annular
region of the optical element 12. However, in this case, the periphery of
the optical element 12 is often shaded by the iris 26 as it contracts to
narrow the pupil. Because of this, photovoltaic cells 72 disposed around
the periphery of the optical element 12 may receive insufficient light to
power the various other components of the vision prosthesis 10. As a
result, it becomes preferable to dispose the photovoltaic cells 72 in an
annular region having a radius small enough to ensure adequate lighting
but large enough to avoid excessive interference with the patient's
vision.

Modifications for Phakic Patients

[0066] In a patient who suffers from presbyopia (in the presence or
absence of myopia, hyperopia, and/or astigmatism), correcting the eye for
distance vision may not correct the eye for near vision. In such cases,
one option is to remove the natural crystalline lens and to use an
aphakic vision prosthesis as described above. An alternative is to avoid
surgery to the natural crystalline lens and to instead use a phakic
vision prosthesis.

[0067] The aphakic vision prosthesis and procedures described above can be
used in a phakic vision prosthesis with some modifications. With a
patient's natural crystalline lens intact, various portions of the
optical element 12 may be positioned in any of a variety of locations
(e.g., between the natural crystalline lens and the iris, in front of the
iris, hooked to the iris, in the pupillary plane, in the cornea, or as a
contact lens). Components such as the range-finder 18 should be
positioned to measure electrical or mechanical stimuli without causing
injury to the natural crystalline lens, zonules, or ciliary body.

[0068] In a phakic vision prosthesis it is desirable to compensate for any
residual accommodation provided by the natural crystalline lens. This
residual accommodation can cause changes in wavefront aberrations for
different distances-of-regard. In addition, changes to the natural
crystalline lens (e.g., in flexibility or gradient of index of
refraction) may occur over time. These and other changes can be
compensated for by changing wavefront data, in the case of embodiments
having programmable wavefront correction, or by changing the shape of the
ablated surface, in the case of embodiments that use a wavefront
component 13.

[0069] It is to be understood that while the invention has been described
in conjunction with the detailed description thereof, the foregoing
description is intended to illustrate and not limit the scope of the
invention, which is defined by the scope of the appended claims.